1. Field of the Invention
The present disclosure relates to an overcurrent relay applied to a molded case circuit breaker, or the like.
2. Background of the Invention
In general, a protecting relay is a device that monitors a state of an electric power system, and when an accident occurs, the protecting relay detects the accident and operates a breaker to quickly separate an accident section to minimize a section affected by the accident.
Among protecting relays, an overcurrent relay is a protecting relay operating when an input current is equal to or greater than a pre-set value. Overcurrent relays have been used in various fields to protect devices and lines from an overload, a short-circuit, and grounding.
An overcurrent relay includes a plurality of setting knobs in an electronic circuit board to set a reference value with respect to a fault current and a trip operation time in the event of a fault current. The setting knobs include a setting knob for setting long-time limit reference values, a setting knob for setting short-time limit reference values, and a setting knob for setting instantaneous reference values.
The long-time limit reference values include a reference current value set to correspond to 80% to 100% of an allowable rated current and a trip operation time value set to range from 10 seconds to hundreds of seconds in case a current corresponding to the reference current value flows in a circuit. The short-time limit reference values include a reference current value that is approximately double of an allowable rated current and a trip operation time value to be within one second in case a current corresponding to the reference current value flows in a circuit. The instantaneous reference values include a reference current value set to be two-fold to tens of fold of a rated current in case an instantaneous current is very high due to a short-circuit of a load, a stroke of lightning, or the like, and a trip operation time value set to be generally within 50 milliseconds in case a current corresponding to the reference current value flows in a circuit.
In case of an overcurrent relay used as a trip device in a prior art MCCB, when a function is altered, a program and a PCB are modified to obtain an intended product.
FIG. 1 is a partially enlarged view illustrating a setting unit of an overcurrent relay in the prior art air circuit breaker (ACB), in which a plurality of setting knobs 41b are disposed to be spaced apart from one another in a setting unit 4b of the overcurrent relay. A setting knob 4b′ is provided to set a long-time limit trip operation time in the event of an overcurrent. Here, a trip operation may be turned off by rotating the setting knob 4b′ (a trip operation OFF position is indicated in the circle).
The ACB and the MCCB have a function of turning off an overcurrent trip operation in case of a long-time limit.
Here, overcurrent relays (OCRs) of the ACB and the MCCB have the trip operation conditions set using the same program. However, a trip operation OFF function of an MCCB in case of a long-time limit is against the application standards of Underwriters Laboratories Inc. (UL). In other words, an MCCB cannot use a program same as that of an ACB and should use a different program and PCB from those of an ACB.